Rotary shear valve assemblies are commonly used in the HPLC analytical instrument market. These valve assemblies are characterized by relatively long life and high precision fluid delivery. Many rotary valve assemblies are driven by stepper motors which are used for positioning a grooved rotor device to multiple locations on a stator device. Rotor device and stator device components are manufactured of chemically resistant plastic materials such as PEEK, PFA, MFA, and UHMWPE. Additionally, chemical inertness may be achieved through use of ceramic materials with the added benefit of long life and low wear.
Shear valve assemblies may be produced at a very low cost by means of injection molding parts traditionally produced by more expensive machining methods. Such parts include sun, planet and ring gears and a housing containing these components. Significant design and cost advantage can be gained by using injection molded parts in combination with low cost high performance stepper motors.
Solenoid valve assemblies are used in many industries. However, there are limitations with respect to performance that are not simply overlooked in IVD and analytical instrument markets. Most solenoid valve assemblies, for example, are single on/off switch devices controlling a single point of flow. When multiple points of flow control are desired, more than one solenoid valve assembly is therefore necessary. Another problem commonly associated with theses solenoid valve assemblies is an undesirable pumping phenomenon (pulsating flow variation), believed to be associated with coil, bounce, and pressure differential dynamic effects. Furthermore, solenoid valve assembly seats have been known to be susceptible to sticking and leakage problems caused by dirt or by foreign matter lodged on the seat.
To address these issues, such micro-fluidic shear valve assemblies have been mounted directly to fluid distribution manifold devices. In this manner a single shear valve assembly can replace numerous individual solenoid valve assemblies and nearly eliminate pumping phenomenon characteristic of solenoid valve assemblies.
For the most part, however, the direct mounting of shear valve assemblies to the distribution manifold devices have experienced negative effects. For example, in one particular design, epoxy is used to seal the stator device to a surface of the manifold device. Disadvantages in this art can be seen with regard to leakage and cost. The epoxy must be carefully applied between the stator device and manifold device interface, so as not to interfere with the fluid flow thorough the ports of the stator device. Moreover, the stator device and manifold device contact surfaces require costly dimensional tolerances and finishes and leakage has been known to occur at the epoxy interface. Consequently, leakage repair by removal of the stator device cannot be easily accomplished without damage to the manifold device. Often the solution is to replace the entire manifold device, incurring significant costs.
Accordingly, it is desirable to provide a micro-fluidic valve assembly that can be simply and cost effectively mounted directly to a fluid distribution manifold without leakage or operational compromise.